1. Field of the Invention
The invention generally relates to the installation and testing of communications systems which use low and high pass frequency splitters to offer both broadband and narrow band services over a single twisted pair line connection and more particularly to testing the continuity of connections in telecommunications systems which use POTS Splitters in order to offer Plain Old Telephone Service (POTS) and Digital Subscriber Line (DSL) services over a single twisted pair connection.
2. Brief Description of the Prior Art
The Internet is a worldwide interconnection of computers that has made a vast array of multimedia, audio, video, graphics and text information available to home users on their computers, game consoles and other digital devices. This Internet content typically requires millions of bits of digital data to be transmitted from or downloaded to the user""s digital device. The voice telephone network built up over the past 125 years provides a comprehensive physical connectivity between homes and has become used as a way of linking home users to the Internet. However, the telephone system was designed for narrow band voice communications, and the all important xe2x80x9clast milexe2x80x9d connection to customers homes was built of twisted pair copper wire. Conventional voice-band data modems using these twisted pair telephone lines to transmit data at less than 56 kilobits per second. The user""s ability to quickly obtain and view information using such modems is substantially limited.
To try and meet their customers"" desire for high-speed connections to the Internet, telephone companies have attempted to upgrade their networks and add higher speed services such as Asymmetrical Digital Subscriber Lines (ADSL) and Digital Subscriber Lines (DSL). ASDL, as described in for instance the International Telecommunication Union (ITU) Standards Document ITU G.992.1 consists of a pair of Discrete Multitone (DMT) modems, one at each end of a twisted pair subscriber loop, with band splitters at each end to provide isolation between a high frequency spectrum (above 24 KHz) used for data transmission and lower frequencies (0-4 KHz) used for voice transmission or Plain Old Telephone Service (POTS). These modems use DMT technology to provide high data bandwidth and the ability to adapt the data rate at startup to match the transmission and noise characteristics of each individual subscriber loop. The band splitters at each end are usually called POTS splitters.
These high-speed digital transmissions were never envisaged by the telephone systems original designers. Consequently much of the legacy engineering, including the light gauge copper cable, as well as typical enhancement such as load coils, filters and bridged taps, provide significant obstacles to providing such high speed services. Moreover, ADSL and DSL are complex technologies involving sophisticated equipment and software that can require skilled technicians to install and maintain. It has been reported by R. Suehring in Xchange Magazine that 85 percent of DSL and ADSL installations are unsuccessful on their first attempt, and that amongst the significant causes of the failure are connectivity issues. SUEHRING, R. xe2x80x9cStreamlining DSL,xe2x80x9d Xchange, July 2000. Retrieved from the Internet.
When a customer orders a high speed ADSL data link, rewiring typically occurs at the telephone company""s Main Distribution Frame. In this rewiring the existing subscriber connection to a POTS circuit has to be rewired to a POTS splitter, then outputs from the splitter connected to the original POTS circuit and to an associated ADSL circuit. A standard method of testing connectivity is a simple resistance test using DC current. POTS splitters are simple telephone devices which function by using capacitors to block DC current and ringing from reaching the ADSL data line and inductors to block high-frequency ADSL signals from reaching the POTS circuit. Having DC blocking capacitors in the splitter prevents the use of simple resistance measurements to test whether or not the rewiring from the Main Distribution Frame has connected the splitter to the correct ADSL line.
What is needed is a simple apparatus and test that will allow checking of this rewiring across the blocking capacitors and inductors of a POTS splitter.
Briefly described, the purpose of the current invention is to provide a simple means of testing the connectivity of wiring through a capacitor/inductor frequency splitter so as to be able to quickly test and verify the set up of a communications system that uses such a splitter to provide subscribers with both broadband and narrowband services over a single physical connection.
In one embodiment of the invention, a simple means is provided to test the cross connect wiring of a communications system which uses a POTS splitter to separate the high frequency ADSL data from the DC and low frequency signals of a incoming telephone line. The simple means includes a low to mid frequency signal, such as but not limited to, a 1 KHz tone signal, fed at sufficient amplitude through the higher frequency or ADSL connection of the POTS splitter so that even after attenuation by the capacitance and inductance blocking filters within the POTS splitter, the resultant signal is detectable by a suitably sensitive detector connected to the associated POTS circuit.
In one embodiment of the invention, the input test signal is pulsed or applied intermittently so that it can be detected even in a system where the attenuation has significantly degraded the signal to noise ratio. Detection is done by simple correlation, i.e. by making sure that the detected signal is present only when the test signal itself is present.
The invention may be more fully understood by reference to the following drawings.